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Au dio L ab s Tube DAC 3.5B Assembly Manual February 10, 1997 SHELDON D. STOKES 103 Windy Cove Apt I Hampton VA 23666 [email protected] http://www.clarkson.edu/~stokessd Table Of Contenets: Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 3 Theory Of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 3 Board Etching Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 6 Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 7 Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 10 Component Outlines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 12 Ground Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 13 Signal Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 14 Wiring the Circuit Board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 15 Digital Filter Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 16 Customizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 16 Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 17 2 Introduction: The purpose of this manual is to be a guide to the proper assembly and maintenance of your Tube DAC. The board has been carefully laid out and constructed to make assembly easy and straightforward. The DAC itself has been designed to be very robust and to give years of trouble free service. Theory of Operation: This DAC consists of four separate parts, the decoder, the digital filter, the digital to analog conversion, and analog gain and buffering. The first part, is the decoder. The digital audio data enters the DAC via a coaxial input BNC connector. It uses the standard SPDIF standard 75 input impedance, but the DAC uses a BNC connector rather than an RCA jack. The data stream is capacitively coupled to a pulse transformer. The pulse transformer reduces common mode noise dramatically, and improves the performance of the input circuitry. The output of the pulse transformer goes to the input pins of the decoder chip. It also has a 75 resistor in parallel with the chip to set the input impedance. The decoder chip reconstructs the various clocks from the serial data stream. This chip uses a PLL (phase locked loop) to generate the clocks from the data stream. Sampling and status information are also extracted from the data str